This invention relates generally to thruster systems used particularly for slow speed maneuvering of a marine vessel. More specifically, this invention relates to a compact thruster system designed for energy-efficient generation of one or more directionally oriented water jets used to maneuver and/or propel the marine vessel.
Boat thruster systems are generally known in the art for use in close-quarter maneuvering of a marine vessel. Such thruster systems are designed to generate a flow of water discharged from one side of a boat hull, resulting in a substantial hydraulic reaction force applied to the vessel for improved close-quarter maneuvering. In one traditional form, the thruster system comprises a relatively large diameter propeller mounted within a correspondingly sized transverse opening or tunnel formed in the boat hull, wherein the propeller is adapted to generate a substantial mass flow of water directed to one side of the vessel in accordance with the direction of propeller rotation. While so-called tunnel thrusters of this type provide significant advantages in close-quarter vessel maneuvering, especially upon approach to or departure from a dock, the thruster system occupies a large volumetric space within the hull of the vessel. Moreover, large openings must be formed in the vessel's hull, usually in a dry dock environment, to accommodate installation of the requisite large diameter flow tunnel. As a result, tunnel thruster systems exhibit significant disadvantages with respect to system size and installation cost.
In recent years, alternative and comparatively more compact thruster systems have been designed wherein a high capacity water pump delivers water for discharge as high velocity jets through relatively small nozzles mounted at opposite sides of the vessel's hull. See, for example, U.S. Pat. Nos. 4,056,073; 4,214,544; and 4,455,960. In these thruster systems, the pump draws in water through a downwardly open intake formed in the hull. The water is delivered from the pump through a diffuser and directionally controlled vanes for discharge flow through one of the nozzles, resulting in an hydraulic reaction force which is effective to assist in vessel maneuvering. Water jet thruster systems of this type beneficially occupy significantly less space within the hull of a vessel, and may be installed without requiring large holes to be formed in the hull. Moreover, additional directional vanes and/or additional discharge nozzles may be employed to generate reaction forces in a fore-aft direction for vessel propulsion in close-quarter maneuvers, or as an auxiliary drive source in the event of main engine failure. However, the thrust generation capacity of a water jet system has been relatively inefficient from an energy standpoint, in comparison with tunnel thruster systems.
There exists, therefore, a significant need for improvements in thruster systems of the water jet type, particularly with respect to improving the efficiency of thrust generation. The present invention fulfills this need and provides further related advantages.